388 



SOME REPRESENTATIVE INSECTS 



The ichneumon flies (cf. Fig. 196 h and Fig. 200) somewhat 

 resemble the gall-flies save that their larvae are parasites in insects 

 instead of living in plants. The reader has perhaps seen cater- 



FiG. 200. — A study in ecology: an ichneumon, one of the Order Hymenoptera, 



laying its egg upon an aphid, Order Hemiptera, and the emergence of the adult 



parasite after completing its development within the aphid. 



(After Webster, from Circular No. 107, New Jersey Agr. Exp. Sta.) 



pillars that were covered with minute cocoons and evidently 

 dying. In such instances the caterpillar has been attacked by 

 an ichneumon which, in laying its eggs, has attached them to the 



^,0^ surface of its host or, more rarety, 



y ';^'y has placed them within the body. 



( When the ichneumon larva hatches 



^^_\^^^^^; .-^> it burrows within the body of the 



i ^sr^^k a" " host and lives as a parasite until its 



time of metamorphosis, when it 

 comes to the surface and spins the 

 cocoon that is seen externally. From 

 this the adult fly emerges, while 

 the host dies, if it has been heavily 

 parasitized. There are many va- 

 riants in this cycle in different 

 species, but the essential features 

 are the same. We think of the 

 ants, bees, and wasps as constitut- 

 ing a majority of the Hymenoptera, 

 although it is a fact that the para- 

 sitic species far outnumber these better-known forms. 



The wasps may be subdivided into the soHtary species, in which 



Fig. 201. — Solitary wasp, Sphc- 

 cius, flying with a cicada which 

 it has paralyzed and is carrying 

 to its nest {cf. Fig. 202). 



(After Riley, Bulletin No. 71, U. S. 

 Bur. Entomology.) 



